1. Field of the Invention
The present invention relates to a track jumping scan control device for controlling an optical beam track jumping scan and a track searching device for searching a track in an optical recording/reproducing apparatus for recording and reproducing information on an optical disc such as DVD-RAM in land track/groove track recording modes.
2. Description of the Related Art
In order to respond to a demand that a capacitance be increased which has been rising in recent years, high density optical disc formats of various types have been proposed. One of them is recited in No. H07-296394 of the Japanese Patent Applications Laid-Open. According to the format, a track in a circumferential direction is divided into a plurality of sectors, a header region having address information is provided at the top of each sector, and a recording region is provided subsequent to the header region. Further, the recording region comprises a land track having a protruding shape and a groove track having a recessed shape, polarities of which for tracking control are inverted, and these tracks are alternately provided in a radial direction. The address information of the header region is called CAPA (Complementary Allocated Pit Address) and comprises pits previously formed between the land track and the groove track (prepits). The pits thus constitute the address information so that an optical head can extract the address information in both the groove and land tracks.
In an optical recording/reproducing apparatus for recording and reproducing information on the optical disc, a focus control in which an optical beam is constantly in a predetermined focused state on a material film and a tracking control in which the optical beam can constantly and accurately scan a predetermined track are executed. Further, a track jumping scan in which the optical beam jumps from one track to another is executed when it is necessary for the optical beam to transfer from an arbitrary track to another. The track jumping scan is described referring to FIG. 20.
FIG. 20 is a timing chart of signals for executing the track jumping scan. In FIG. 20, the tracking control is OFF at timings t51-t53, and the tracking control is ON at and after the timing t53. (a) denotes a CAPA signal in the header region, (b) denotes a tracking error signal, (c) denotes a zero-crossing detecting signal for detecting zero-crossing of the tracking error signal, (d) denotes a tracking drive signal including an acceleration drive pulse for accelerating the optical beam toward an adjacent track and a deceleration drive pulse for decelerating the optical beam.
As shown in (a), the CAPA signal rises at a timing t50, and at the same time, the tracking error signal crosses the zero level as shown in (b). Then, the zero-crossing detecting signal rises as shown in (c). As shown in (d), at the timing t51 after a predetermined time has passed since the rise of the zero-crossing detecting signal, the optical beam is moved toward a targeted track at an increasing speed by the acceleration drive pulse having a rectangular shape. After the acceleration drive pulse is terminated, the optical beam is moved by inertia. At a time point when the optical beam falls on a substantially intermediate point between the targeted track and another track adjacent thereto in the radial direction of the disc, that is the timing t52 in (d), the optical beam is decelerated by the deceleration drive pulse having the same rectangular shape as that of the acceleration drive pulse but an inversed polarity. At and after the timing t53 when the deceleration drive pulse is terminated, the tracking control is ON, however, the tracking control is destabilized between the timings t53 and t55 since disturbances are generated in the drive signal under the influence of the CAPA signal in (a) at timings t54-t55 as shown in a waveform of the drive signal in (d). Immediately after the tracking control is operated again at and after the timing t53, the control is in a transient state and large errors are generated in the control operation, which makes it impossible for the optical beam to be stably drawn into the targeted track when the disturbances in the header region are superposed.